Sound amplifying apparatus for telephone circuits



D. c. BEATTY 2,786,099

soUND AMPLIFYING APPARATUS FOR ,TELEPHONE CIRCUITS March 19, 1957 INVENTOR DONALD C. BEATTY ATTORNEY AMPLEFYING APPARATUS FOR LTIHJEPHONECIRCUITS soUND The presentwapplication covers a structure generallyanalogous to those in U. S. Patents No. 2,525,763 and No. 2,539,565,granted to me on October 17, 1950, and January 12, 1951, respectively,and isa continuation 1n part of my copending, application Serial No.193,988, filed November 3, 1950. j

The invention relates toa novel electrical apparatus for amplifying thevoice or other sound made by a party calling a telephone circuit towhich the apparatus 1s .attached, and for transmitting to the callingparty the voice or sound made by any party or parties within theacoustical range of the device.

The invention also relates to improved electrical apparatus by means ofwhich the operator is enabled to cause it to automatically functionwithout his further action or attention, or, by adjustment to cause thedevice to remain in the inoperative condition until he elects to causeit to function or operate.

By way of background, it may be noted that the desirability of apparatusof the character mentioned is readily apparent as being in the interestnot only of the general public in conducting its individual or personalaffairs, but also of individuals of the many professions, business rms,organizations and departments of state and federal governments. Suchapparatus fills a long felt need in connection with the conducting ofones personal and business affairs and in the conducting of business ingeneral, both private and government. This is so because in the normaluse of the telephone over which a high percentage of personal andbusiness affairs is conducted, the user thereof must go to thatinstrument and remain in its immediate vicinity while utilizing one ofhis hands to hold the ear piece and microphone of the instrument to hisear and mouth respectively. This makes it difficult, if not impossiblefor the user at the same time to use his hands and head in a normalmanner while for example, copying the transmitted intelligence, makingof mem- Granda, the searching through notes, files or papers for data orto move away from the very immediate vicinity of the telephoneinstrument.

lt is, accordingly, the main object of the present invention to provideapparatus which will be capable of eliminating the current diicultyabove described.

Other important objects are to provide apparatus as stated that will besimple and compact; will be attachable to a conventionally installedtelephone instrument or connecting wires thereto; will be capable ofinstallation with a minimum expenditure of time and effort; will offerno problems in the use thereof by the parties; will be economical inconstruction; and by election of the user, will be automatic inoperation or remain inoperative until manually caused to function oroperate.

In simple terms the invention, automatically or by manual control of theoperator, operates over a telephone circuit similarly to the manner bywhich a conventional office intercommunication set operates to andbetween nearby oices. The apparatus permits full two-way connited Statesarent versations without the inconvenience of manual or other circuitswitching to permit either listen or talk functions of the device; whenconnected to a telephone circuit and adjusted to the automatic positionand with proper electric power connected to the apparatus, the firstring of an incoming telephone call starts the apparatus. Without in anymanner touching a nearby telephone which may be connected to the sametelephone circuit, or in any manner lifting the receiver of such atelephone, the voice of the calling party is amplied and emitted fromthe loud speaker of the device with any selected volume of sound. Aperson or persons within the acoustical range of the device may thenconverse freely in a normal manner with said caller, and, upontermination of the conversation, or sooner, the calling party, byhanging up the receiver of his telephone instrument, will cause theapparatus to return to its nor-mal standby or olf condition. Also, theoperator of the device may, -athis election during norm-al use of thetelephone, cause the apparatus to begin functioning and thereupon he mayhang up his telephone and continue the conversation by means of theapparatus above described. As in the instant given above, the apparatuswill automatically, following such use, return to the normal standby orofi condition.

With the foregoing and other objects in viewwhich will appear as thedescription proceeds, the invention consists of certain novel details ofconstruction and combinations of parts, hereinafter more fully describedand pointed out in the claims, it being understood that changes may bemade in the construction and arrangements of parts without departingfrom the spirit of the invention as claimed.

In the drawing:

Figure l is a schematic representation or wiring diagram of the instantinvention;

Figure 2 is a wiring diagram of a modied balancing and segregatingnetwork; and

`Figure 3` is -a wiring diagram showing the invention embodied in anintercommunication system.

The description of the apparatus which follows, will be divided intofour (4) lgeneral phases. Each phase pertains to a particular functionperformed by the apparatus, namely:

-Phase l. The manual or automatic control circuit.

Phase 2. The segregating or balancing network circuit. Phase 3. Thevacuum tube voltage amplier receivmg circuit.

Phase 4. The vacuum tube voltage generating transmitting circuit.

PHASE ONE Manual or automatic control circuit Referring to the drawingin detail, L1 yand L2 are leads connected directly 'to an ordinarytelephone cincuit including a telephone, not shown, and its signaldevice, also not shown.

Extending respectively from the leads L1 and L2 are the leads L53 andL3, that are connected to the coil of relay S2, with lead L3 having inseries connection therewith condenser C10, lead 54 and manually operatedswitch S1. Switch S1 is left in the open position for manual control ofthe device. Switch S1 is placed in the closed position for automaticoperation of the apparatus.

Through the ordinary telephone circuit referred to above but not shown,there is adapted to pass a sustaining Adirect current, as for example,during ordinary conversation between a calling and a called party.

On other occasions, a current differing from the sustaining currentreferred to, is caused, automatically or otherwise, to pass through thetelephone circuit to which leads L1 and L2 are electrically connected,for the pur- 3 pose of causing actuation of a signal device such as abell. This can be termed an intermitten current and is exemplified bythe sending of alternating current surges at intervals through thetelephone circuit for the purpose of ringing the bell, not shown.

Assuming that the switch S1 is in the closed position, the intermittentalternating current owing through or over leads L1 and L2 will not onlyactuate the signaling device but will also flow through the coil windingof and energize relay S2. This will close the normally open switchcontacts of relay S2, said relay being respondent to said intermittentcurrent, so as to close a circuit including lead 8, the secondarywinding of transformer X1, lead 16, through the normally closed switchcontacts of relay S4, lead 15, lead 14, llead 13 to one side of the coilwinding of relay S3, lead 12, the other side of coil of relay S3. lead11 and back through the closed switch contacts of relay SZ to completethe closed circuit.

YWith switch S7 closed and the primary winding of transformer X1connected to an appropriate source of electric power, the result of theabove described closing of switch contacts of relay S2 will be thatrelay S3 is energized and closes its three normally open switch contactsA, B, and C. The closing of these 'switch contacts, among other things,places a short circuit across the switch contacts of relay S2.Therefore, there will be closed a circuit not by means of the closedswitch contacts of relay S2 but by and including the closed switchcontacts A of relay S3, lead 10, lead 8, secondary winding oftransformer X1, lead 16, normally closed switch contacts of relay S4,lead 15, lead 14, lead 13 to `one side of coil winding of relay S3, fromthe other side of coil of relay S3, lead 12, lead 11, lead 9, and backto complete the closed circuit to switch contacts A f relay S3. Theresult will be to hold relay S3 energized, without possibility of itsbeing affected by any intermittent opening and closing of switchcontacts of relay y S2 under the action of the intermittent currentreferred to.

The closing of switch contacts B and C of relay S3 closes an electricalcircuit to and including leads L1 and L2 as follows: L1, lead 53, closedswitch contacts B of relay S3, lead LS to one side of the coil windingof direct current relay S5, the other side of the coil winding of directcurrent relay S5, lead L4, closed switch contacts C of relay S3, to leadL2 and thus to close the circuit. With the closing of this circuitdirect current relay S is energized, among other things, and closes itsnormally open switch contacts. These closed switch contacts are thusplaced in short circuit across the normally closed switch contacts ofrelay S4. The closed circuit energizing and making operable relay S3,inclu-ding one side of the coil winding of relay S3, lead 12, lead 11,lead 9, closed switch contacts A of relay S3, lead 10, lead 8, thesecondary winding of transformer X1, lead 16, closed switch contacts ofrelay S4, lead 15, lead 14, lead 13, and back to the other side of thecoil winding of relay S3, is augmented and maintained closed by theclosed switch contacts of relay S5 being placed in short circuit acrossthe normally closed switch contacts of non-energized relay S4.

With the energizing of relay S3 and the closing of its switch contacts Band C and the resultant connection to leads L1 and L2 of the leads L5and L4 respectively, a further closed circuit is established to andincluding lead L1 and *lead L2 (this closed circuit is in shuntconnection with and across the coil winding of direct current relay S5which is likewise in a circuit closed to and including lead L1 and leadL2). The closed circuit so established is: lead L1, closed switchcontacts B of relay S3, lead L5, lead L7, one side of the primarywinding of transformer X5, the other side of primary winding oftransformer X5, lead 29, resistance R5, lead 27, lead L6, lead L4,closed switch contacts C of relay S3, and return to lead L2 to close thecircuit.

The closing of the latter circuit, above described, places an electricalload composed of resistance R5 and the primary winding of transformer X5across telephone leads L1 and L2. The making of this electricalconnection brings about the operation of devices, not shown, that resultin the cessation of the intermitten `alternating current referred to inthe telephone circuit to which leads L1 and L2 are connected. Theactuation of these devices likewise result in the establishment andstabilizaf tion of the sustaining current in said telephone circuit andin the leads L1 and L2. The stabilized conditions of said circuit willthereafter persist so long asfresistance R5 and primary winding oftransformer X5 remain in shunt across said circuit, or until saidcircuit is interrupted either manually, Such as by changing the circuitcharacteristic by hanging up the receiver of a telephone connected insaid circuit, or automatically.

it has been previously described how the circuit to and including directcurrent relay SS and telephone leads L1 and L2 is closed by theenergization of relay S3. With the stabilization of the sustainingdirect current in leads L1 and L2 coincident with the operation of relayS3 and the resultant cessation of the intermittent alternating current,the normally open switch contact points of direct current relay S5 closeas before described. These switch contact points continueto remain inthe closed position until deenergization of relay S5 as hereinafterdescribed.

From the description so far provided, it will be seen that with theapparatus supplied with appropriate electric power, with switch S1 inthe closed position, and with leads L1 and L2 connected to a telephonecircuit as previously described, a call placed to the telephone circuit,to which the apparatus is connected will, on the first surge of theintermittent ringing current, energize the relay S2 so as to momentarilyclose its normally open switch contact points; that the momentaryclosing ot' the switch contact points of relay S2 closes an electricalcircuit including a source of electric power and the coil winding ofrelay S3; that the closing of switch contact points B and C of relay S3completes and closes a circuit to and including a telephone circuit, notshown, and to and including said circuit and leads L1 and L2 and thecoilwinding of direct `current relay S5; and, that the electrical loadof resistance R5 and the primary winding of transformer X5 in shuntcircuit across the coil winding of relay S5 is consequently imposed as aclosed circuit to and including lead L1 and lead L2 and the telephonecircuit to which these leads are connected. It will also be seen thatimmediately upon the above things taking place, the intermittent currentis caused to cease and to be thereupon replaced with the stabilizedconditions of the sustaining current.

When the circuit including the relay S3 was lirst closed, electricalcurrent will have passed through lead 12, the coil winding of delayedaction relay S4, and lead 13. The relay S4 is of a type, Well known inthe art, that is adapted to operate after a delay following thecompletion of an electric circuit through its iield winding.

When, after such delay, relay S4 actuates, it operates to open itsnormally closed switch contacts. These switch contacts are connected toleads 16 and 15 respectively and formed a part of the initially closedcircuit including the coil winding of relay S3 and a source of electricpower previously described. With the opening of the normally yclosedswitch contact points of delayed action relay S4, the closed circuit toand between the source of electric power and coil windings of relays S3and S4 is maintained in a closed circuit condition bccause of the closedcondition of the switch contact points of relay S5, previouslydescribed. The closed circuit thus maintained includes lead S, lead 10,closed switch Vcontact points of- A of relay S3, lead 11, lead 12, oneside of the coil windings of relay S3 and delayed action relay S4, theother side of the coil windings of relay S3 and delayed action relay S4,Vlead 13, lead 14, lead 15,

'return to said normal open position.

closed switch contacts of relay S', lead 16, one side of secondarywinding of power transformer XLthe other side of that winding to lead t3and thus to complete and `close the circuit.

flowing through or over that closed circuit of the sustaining current`will persist in maintaining relay S5 energized and in an operatedcondition so long as the sustaining current is uninterrupted.

Upon the interruption, changing of polarity, or any similar change inthe sustaining current in circuit to and including leads Ll and L2,through the field winding of relay S5, the relay S5` will bedecnergized, thus releasing its switch contact points, which return tothe normally open position.

Accordingly, the opening of. switch contact points of relay S5 thusopens the closed circuit including a local source of electric power, ofwhich those contact points are a part. With the described closed circuitthus broken or opened, relays S3 and S4 become deenergized und releasetheir respective operated switch contact points. The switch contactpoints of relay S3\ therefore revert to their normally open ppsitionswhile those of relay S4 revert to their normally closed position. rlfhisis so because the switch contact points of delay acting relay S4 and theclosed circuit of which those switch Contact points had been a part hadbeen maintained in closed circuit by the closed switch contact points ofrelay S5, said contact points of relay S5 being connected in shuntacross the switch contact points of relay S4 as hereinbefore described.p

From the described circuit above provided, it will be observed that withswitch S7 closed and the apparatus connected to a source of electricpower by leads to the primary winding of transformer Xl, upon the rstsurge of intermittent current over leads Ll and L2, relays S2, S3, S5and S4 will, in turn become energized and operate; that upon suchoperation of those relays the intermittent alternating current will becaused to desist and be replaced with the sustaining direct current inclosed circuit including lead L1 and L2, L4, L5, L6, L7, relay SS,primary winding of transformer X5, lead 29, resistance R5, lead 27, leadL6 to complete and close the circuit; and, that upon interruption ofsaid sustaining current the relay S5 is deenergized and its switchContact points are caused to return to their normally open position, andfurther, that upon the opening of switch contact points of the relay S5,the circuit closed to and inciuding those switch contact points is thusbroken resulting in relays S4 and S3 becoming deenergized and returningto their respective inoperative condition. The closed circuit thusopened to the local source of electric power causes the apparatus tocease operating and to return to its original standby or inoperativecondition.

The interruption of the sustaining current may, among other things, becaused by the calling party hanging up his telephone instrument. Suchactioncauses an interruption or change in the characteristic of thesustaining current, and this change in said current to and through thefield winding of relay S5 deenergizes said relay and causes its normallyopen contact points to The illustrated circuits are thus returned totheir original or starting condition. A subsequent call will again, withswitch S7c1osed and the apparatus connected as described, set intomotion the electrical sequences described.

This phase consists of a novel segregating or balancing networkconsisting'of electrical components, in combina tion, in closed series,and shunt connection paths with and including leads L1 and L2 and atelephone circuit, not shown. By the novel and appropriate arrangementof these electrical components, the required balancing is obtained inthe circuits comprising the Phase Two, Phase Three and Phase Fourportions of this invention and the telephone circuit, not shown, towhich it is connected. The attenuation and electrical balancing of theseveral circuits of this device so obtained, permits the joint andapproximate simultaneous connection to a common pair of leads L6 and L7of a vacuum tube Voltage generator or transmitter (Phase Four) and avacuum tube voltage amplifier or receiver (Phase Three), in complementto each other and without impairment of operation of the severalelectrical circuits comprising this invention. This is accomplishedwithout introducing undesirable electrical changes or irregularitieswithin 'the apparatus or within the telephone circuit to which, by meansof and including leads L1 and L2, the device is connected.

The electrical components making up the Phase Two portion of this noveldevice consists of resistances R4, R5, R6, and R7, condensers C3 and C4,and inductances X4 and X5, the latter being the secondary winding oftransformer X4 and primary winding of transformer X5 respectively.Connected in circuit as hereinafter described, impulses carrying soundvoltage flowing from the Phase Four circuits, as shown, are zeroed out,cancelled and made ineective with respect to the secondary winding oftransformer X5 of the vacuum tube voltage amplifier receiver hereinafterdescribed as the Phase Three portion of this invention.

The owing of the sound impulse carrying voltage generated by theillustrated circuits shown as 1Phase Four, are inductively passed fromprimary winding of transformer X4 to one side of the secondary windingof lthat transformer, lead L6, lead L4, closed switch contacts C ofrelay S3, lead L2, one side of a telephone circuit to which that lead isconnected, and from the other side of secondary winding of transformerX4, lead 26, condenser C4, lead 26, resistance R7, lead L7, lead L5,closed switch contacts B of relay S32 lead Ll to the other side of thetelephone circuit, not shown, to which said lead is connected and thusto complete the closed circuit.

Connected to one side of the secondary winding of transformer X4 and inshunt connection between lead L6 and L7, is the lead 27, resistance R6and condenser C3 which, in turn is connected to lead L7 and to one sideof the primary winding of transformer X5. Connected to that same sidelof the primary winding of transformer X5 and to lead L7 is theresistance R7, lead 26, condenser C4, lead 26 which is connected to theother side of the secondary winding of transformer X4. These circuits,so described, form the paths for the flowing or passage of the soundimpulse carrying voltage generated (transmitted) by the Phase Fourportion of the device to and including the telephone circuit to whichthe apparatus is connected.

From the above it will be observed that any voltages generated by thevacuum tube generator transmitter illustrated as Phase Four circuitshereof, will flow by induction in or through secondary Winding oftransformer X4, lead L6, lead L7, lead L4, lead LS, lead L1 and lead L2,to the telephone circuit to which said latter leads are connected. Y

From the above it will also be observed that the generated voltageswill, with respect to being induced into the secondary winding oftransformer XS and thence into the vacuum tube voltage amplifierreceiver illustrated as Phase Three of this device, be zeroed out orcancelled and will therefore not be effective with or amplified by thesaid vacuum tube voltage amplifier receiver. This is so because thevoltages generated by the vacuum tube voltage -generator transmitterabove described, will, when induced into the secondary winding oftransformer X4, flow or pass from said secondary winding to leads L6 andL7 as above described. The voltages thus generated will not flow or passthrough the primary winding of transformer X primarily because saidvoltages iiow only to one side of primary winding of transformer' X5from the two sides of secondary winding of transformer X4 over leadshaving capacitance and resistance of respective equal Values and, thatthe connecting to lead L7 of these two electrically equal leads cancelsor zeroes out, with respect to transformer X5, voltages flowing from thesecondary winding of transformer X4. Said voltages flow, not to orthrough transformer XS, but instead flow out or over lead L7 and lead L6which form a part `of the circuit closed to and including the telephonecircuit as above described. Secondarily, voltages induced into thesecondary winding of transformer X4 are further prevented from becc tingeffective on or with the secondary winding of transformer X5 andconsequently the vacuum tube voltage amplifier receiver because theother side of the primary winding of transformer X5, lead 29, resistanceRa'- or resistance R5 respectively, offer paths of greater electricalresistance and `delay to such generated voltages induced into andfiowing from the secondary winding of transformer X4. Because of thesefacts, the voltages so generated are ineffective with and upontransformer X5.

Conversely, voltages carrying sound impulses from the telephone circuitto which the apparatus is connected by means of leads Ll and L2, cannotbe effective upon the vacuum tube voltage generator transmitter asillustrated, butV will fiow along a direct electrical path to and willbe effective upon the vacuum tube voltage amplifier receiver describedhereinafter as Phase Three. This is so because such a circuit has beenclosed to the telephone circuit to which the apparatus is connected withand including the following: L2 attached to one side of the telephonecircuit, not shown, closed switch contacts C of relay S3, lead L4, leadL6, lead 27, resistance R5, lead 29 to one side of primary winding oftransformer X5, the other side of primary winding of transformer X5,lead L7, lead L5, closed switch contacts B of relay S3, lead L1 to theother side of the telephone circuit, not shown, and thus to close thecircuit.

The novel balancing and segregating network above described, is thepreferred method of permitting the invention to operate as designed.Other less efficient and effective means may be utilized however formaking the apparatus operable to a lesser `degree of efficiency. To nameone such means reference is made to Figure 2 of the diagram. This ligureillustrates the use of a six winding hybrid coil of balanced proportionsas it would be used for making the invention operable.

With reference to Figure 2 and substituting therein transformers X1 andX6 for transformers X5 and X4 respectively of Figure l, and with leadsL6 and L7, Figure 2 connected to L4 and L5 of Figure l instead of asshown in Figure 1, the siX winding hybrid coil represented as X2, X3,X4, and X5 of Figure 2, will, together with its balancing networkresistor R1 and condenser C1, act to make the invention operable.Although operable with such an arrangement, the apparatus will be lesseicient than by the use of the novel segregating and balancing networkheretofore described.

Y PHASE THREE Vacuum tube voltage amplifier receiving circuit The vacuumtube voltage amplifier, in circuit combination as illustrated in Figurel, is a novel arrangement of vacuum tubes T3, T4 and T5 and associatedinductances, resistors, and capacitors, a source of electrical power anda loud speaker. While such a voltage amplifier is Cil not new to theart, its use in combination described, is both original and novel.

With reference to Figure l and to Phase Three thereof in detail, withswitch S8 closed and the primary Winding of transformer X2 connected toan appropriate source of electrical power, current will be induced intothe secondary windings of that transformer. With the two secondarywindings of transformer X2 connected as illustrated, leads 46 and 47from one such secondary Winding are connected to the two platesrespectively of rectifier tube T5. With the other secondary winding oftransformer X2 connected by leads 44 and 45 respectively to the heateror filament of tube T6, the tube will function to rectify into positivedirect current the alternating current so delivered to it from secondarywinding of transformer X2. The negative side of this direct current isdeveloped as illustrated, by grounding to the common ground of theapparatus, the mid or node point of each of the secondary windings oftransformer X2. Lead 43, connected to the cathode of tube T5, carriesthe high potential positive direct current to the plate element ofoutput tube T4 via lead 41, primary winding of loudspeaker LS couplingtransformer X6 and lead 40. Connected to lead 43 is a conventionalfilter and voltage reducing network consisting of condensers C8, C9 andresistor RZ. Appropri- 'ate resistors and capcitors in correct andconventional circuit to the other elements of output tube T4 and firstamplifier tube T3, will, when voltage carrying sound impulses is inducedinto secondary winding of transformer X5 from its primary winding, causesuch voltage to be amplified and emitted in a greater or lesser amountfrom loudspeaker LS. The extent of volume of sound so emitted isadjustable by the operator of the device by means of the adjustablevolume control resistor R10 provided for that purpose, said adjustablemeans controlling the amount of input voltage to the grid element ofoutput tube T4 which in turn emits a greater or lesser amount of suchvoltage carrying sound impulses to loudspeaker LS, in circuit, With aresulting greater or lesser sound output by said loudspeaker.

PHASE F OUR The vacuum tube voltage generating transmitting circuit Thevacuum tube voltage generating or transmitting circuit, in circuitcombination as illustrated in Figure l, is a novel arrangement of vacuumtubes T1, T2 and T5 and associated inductances, resistors andcapacitors, a source of electrical power and a microphone. While such avoltage generator is not new to the art, its use in cornbinationdescribed, is both original and novel.

With reference to Figure l and to Phase Four thereof in detail, withswitch S8 closed and the primary winding of transformer X2 conected toan appropriate source of electric power, current will be induced intothe secondary windings of that transformer. With the two secondarywindings of transformer X2 connected as illustrated, proper andappropriate direct current voltage will be supplied, not only to theelements of voltage generating vacuum tubes T1 and T2, but likewise toresistors, capacitors, inductances and microphone in circuit asillustrated, comprising the Phase Four portion of Figure l.

By the means above provided, it therefore logically follows that whenaudible sound waves are impressed upon the diaphragm of microphone MIC,such sound waves will, in the form of increased voltage, be impressedupon the grid element of first voltage amplifying (generating) tube T1.By the peculiar functions of that tube, such voltages will be increasedand again impressed, by appropriate circuits, on the grid element ofsecond Voltage amplifying (generating) tube T2. Again, by the peculiarfunctions of that tube, such increased or generated voltages will owfrom the plate element of that tube, lead 24 and, among other thingswill ow to and through the arenoso primary winding of transformer X4.These sound im- .pulse carrying voltages will be induced into thesecondary winding of transformer X4 in closed circuit, as hereto- -foredescribed, to and including the telephone circuit to which the apparatusis connected by its leads L1 and L2.

From the above and other description provided, it is voltages carryingsound impulses, that such voltages are amplified (generated) as theyprogress in circuit combi- 'nat-ion through the vacuum tube voltagegenerating transmitting circuit abovedescribed and, lthat by circuitcombination those increasedk voltages are impressed into or upon 'thetelephone circuitnot shown, to which the apparatus is connected by leadsL1 and L2. Also, as previously described, such amplified or generatedtransmitting voltages will, with respect to the Phase Three amplifierreceiving"circuits above described, be zeroed out, cancelled andineffective upon said Phase Three circuits.

While the description above provided describes the preferred use of theinvention in conjunction with a telephone circuit, not shown, asecondary and further novel use of the apparatus is claimed.

Figure 3 illustrates two loudspeaker/microphone units LS-l and LS-2which may, in circuit, be in any nominal quantity. By appropriatecircuits, one of which is illustrated, these may be connected in circuitto the Phase Two, Phase Three and Phase Four portions of the apparatus,Figure l. Such loudspeaker/microphone units, as in any conventionalintercommunication device, may be physically located at places remotefrom the said phase portions of the apparatus. By connecting lead L6 andL7 of Figure 3 to lead L6 and L7 respectively of Phase Two, Figure 1,and by disconnecting leads L4 and L5 from L6 and L7, Figure 1, and withthe apparatus e11- ergized by a source of electric power, normal two-wayuninterrupted conversation may be held between persons located at theapparatus and at any one or more of the remotely locatedloudspeaker/microphone units. By an appropriate switching arrangement,not shown, such conversations may be by and between a single individualor multiple loudspeaker/microphone units remotely located from theapparatus.

I claim: l

l. A sound amplifying apparatus of the class described, comprising: apair of telephone leads for connection to a telephone instrument toprovide intelligence transmission paths between a caller and a callee; abalancing and segregating network including first and second transformerwindings at opposite sides thereof, a pair of leads respectivelyextending from one end of the respective windings, a first resistanceand condenser connected in series between said ends of the windings, anda second resistance and condenser connected in series between said oneend of the second winding and the other end of the first winding; leadsconnected between the respective second named leads and the telephoneleads, each of the last named leads including a normally open set ofcontacts; a receiving amplifier including a transformer winding coupledwith the first transformer winding; a transmitting amplifier including atransformer winding coupled with the second transformer winding; andmeans responding to the impression of ringing current on the telephoneleads by a caller for closing both of said sets of contacts to permitthe transmission of intelligence between a caller, and a callee locatedwithin the effective acoustical range of the respective amplifiers.

2. A sound amplifying apparatus of the class described, comprising: apair of telephone leads for connection to a telephone instrument toprovide intelligence transmission paths between a caller and a callee; abalancing and segregating network including rst and second transformerwindings at opposite sides thereof, a pair of leads respectivelyextending from one end of the respective windings, a first resistanceand condenser connected in series between said ends of the windings, anda second resistance and condenser connected in series between said oneend of the second winding and the other end of the first winding; leadsconnected between the respective second named leads and the telephoneleads, each of the last named leads including a normally open set ofcontacts; a receiving amplifier including a transformer winding coupledwith the first transformer winding; a transmitting amplifier including atransformer winding coupled with the second transformer winding; andmeans responding to the impression of ringing current on the telephoneleads by a caller for closing both of said sets of contacts to permitthe transmission of intelligence between a caller, and a callee locatedwithin the effective acoustical range of the respective amplifiers, saidcontact-closing means including a first relay in circuit with said leadsand adapted to be temporarily energized by said ringing current, asecond relay connected in circuit with a source of electrical power andoperative for closing both of said sets of contacts when energized, anda third set of normally open contacts in circuit with the second relayand closed by energizing of the first relay to energize the secondrelay.

3. Apparatus as in claim 2, further including a third relay connectedbetween the second named leads and including a set of normally opencontacts in circuit with said source of power and with the second relay,said last named contacts closing on energization of the-third relay tohold the second relay in an energized condition during the transmissionof intelligence between caller and callee.

4. Apparatus as in claim 3, wherein said network further includes aresistance coupled with the first transformer Winding in shunt acrosssaid telephone leads, to impose an electrical load thereupon effectiveto cause a cessation of the ringing current and a stabilization of asustaining current in the telephone leads.

5. Apparatus of the class described comprising a pair yof leads adaptedfor connection in a sound-impulse- Itransmission circuit to permit thetransmission of intelligence between parties at opposite ends of saidcircuit, said leads being disposed at one end of said circuit; a secondpair of leads; connections between the respective second and rst namedleads including normally opened sets of contacts; a balancing andsegregating network having opposite sides connected to the respectivesecond named leads; a receiving and a transmitting amplifierrespectively coupled inductively to the respective opposite sides of thenetwork; series-connected pairs of resistances and condensers extendingbetween the opposite sides of said network; and means responding to theimpression of an intermittent signalling current for closing said setsof contacts.

6. In an in-out amplier system for one `end of a communicationsapparatus over which sound impulses are transmitted to provide for thetransmission of intelligence -between parties at opposite ends of theapparatus, a pair of leads through which sound impulses are transmitted;a balancing and segregating network having its opposite sides providedwith connections t-o the respective leads, said network including, atopposite sides thereof, first and second transformer windings, a firstcondenser and resistance connected in series between one end of therespective windings, and a second resistance and condenser connected inseries between one end of the first transformer winding and the otherend of the second transformer winding; a receiving amplifier including atransformer winding inductively coupled with the first transformerwinding; and a transmitting amplifier including a transformer windinginductively coupled to the second transformer winding.

7. In a balancing and segregating network for asoundimpulse-transmitting apparatus including a pair of sound impulsetransmission leads, and an amplifying receiver and an amplifyingtransmitter each having a transformer Winding, a pair of leads adaptedfor connection to said 11 12 sound impulse transmission leads; rst andsecond transfurther including a resistance connected at one end toformer windings respectively` connected at one end to the the Erstresistance and condenser and at its other end to respective second namedleads and adapted for conductive the second resistance and condenser.coupling to the windings of said receiver and transmitter respectively;a rst condenser and resistance connected in "5 References Cited in thele 0f this patent series between one end of the first Winding and oneend UNITED STATES PATENTS of the second Winding; and a second resistanceand condenser connected in series between said one end of the 2281255Augqstadt Apr' 28 gz l'irst Winding and the other end of the secondWinding. 236935 1 Hemck Feb 1945 8. A balancing and segregating networkas in claim 7, 10 f

